Prefixing of OFDM symbols to support variable subframe length

ABSTRACT

The present disclosure relates to a first radio node configured for orthogonal frequency division multiplexing (OFDM), comprising a receiver, a transmitter, a processor and a memory storing instructions executable by the processor for causing the transmitter in a first mode of operation with a first subcarrier spacing f1: to transmit a sequence of prefixed OFDM symbols, and in a second mode of operation with a second subcarrier spacing f2: to transmit a sequence of prefixed OFDM symbols, wherein the sequence of transmitted OFDM symbols is aligned with a predefined repeating radio frame, which is common to both the first and second modes of operation, or with an integer multiple of the predefined repeating radio frame; and the first and second subcarrier spacings are related by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/197,678, filed Nov. 21, 2018, which is a continuation of U.S.application Ser. No. 15/544,058, filed Jul. 17, 2017 and issued as U.S.Pat. No. 10,193,724 on Jan. 29, 2019, which is a national phaseapplication of International Application No. PCT/SE2017/050480 filed May12, 2017, which in turn claims priority to International Application No.PCT/CN2016/083213 filed May 24, 2016, the disclosures of each of whichare incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure generally relates to the technical field ofwireless communications, and particularly to radio nodes, methods,computer programs and computer program products for prefixing of OFDMsymbols to support variable subframe length.

BACKGROUND

The upcoming 3rd Generation Partnership Project (3GPP) New Radio (NR)radio-access technology is based on Orthogonal Frequency DivisionMultiplexing (OFDM) and will support multiple numerologies in terms ofsubcarrier spacing, subframe (or slot) length etc. A basic subcarrierspacing f0 and a corresponding subframe design consisting of N OFDMsymbols are used. Other numerologies are then achieved by scaling thebasic subcarrier spacing Δf. For example, by using a subcarrier spacingof 2Δf the corresponding OFDM symbol is half as long as in the originalcase with Δf. The overall subframe of N OFDM symbols will consequentlyalso be half as long as in the original case. Having the possibility fordifferent numerologies can be beneficial in order to support differentservices with different requirements in terms of latency; alatency-critical service requiring low latency can use a highersubcarrier spacing and a correspondingly shorter subframe duration.

To allow for coexistence with Long Term Evolution (LTE), in particularNarrow Band Internet of Things (NB-IoT), it is beneficial to use thesame subcarrier spacing f0 as in LTE and 3GPP has therefore agreed onΔf=15 kHz. Furthermore, the LTE slot/subframe structure is beneficial.In LTE, a slot consists of 7 OFDM symbols where the first OFDM symbolhas a slightly longer cyclic prefix (CP) than the others. Morespecifically, in LTE an OFDM symbol without cyclic prefix is 2048Ts longwhere Ts is the basic time unit, Ts=1/(2048×15000) seconds. The firstOFDM symbol has a cyclic prefix of 160Ts and the remaining six OFDMsymbols in the slot have a cyclic prefix of 144Ts. This OFDM symbol isshown shaded grey in FIG. 1, while the white OFDM symbols have theslightly shorter cyclic prefix.

It is beneficial if the symbol boundaries across different numerologiesare time aligned as this would allow for one “long” OFDM symbol to bereplaced by two (or more) “short” OFDM symbols. One usage of this ismultiplexing of different services, e.g., by “replacing” one long OFDMsymbol in an ongoing transmission with two (or more) short symbols fortransmission of a latency-critical message. This is straightforward whenmoving to higher values of Δf. Each OFDM symbol in the numerology withsubcarrier spacing fi (=(i+1)*Δf) is split into two symbols withsubcarrier spacing fi+1(=(i+2)*Δf) as shown in FIG. 1 too. Note thatthis results in the first two symbols of the 30 kHz numerology in a 0.5ms slot having a longer cyclic prefix than the remaining 12 symbols inorder to maintain the symbol boundary alignment.

It is not unlikely that subcarrier spacings lower than 15 kHz areneeded, e.g., for non-latency critical machine-type communication (MTC)services or for broadcast services. One possibility to achieve this isto use the approach described above with f0 set to the lowest possiblesubcarrier spacing desired, e.g., 3.75 kHz. However, when this structureis scaled to 15 kHz the result would not match the LTE slot structureand as a result degrade the coexistence between NR and LTE.

SUMMARY

In view of the foregoing, an object of the present disclosure is toovercome at least one of the above-described drawbacks of the existingapproaches for simply scaling of numerology while maintaining LTEcompatibility at 15 kHz.

To achieve this object, according to a first aspect of the presentdisclosure, there is provided a first radio node configured fororthogonal frequency division multiplexing (OFDM). The first radio nodecomprises a receiver, a transmitter, a processor and a memory storinginstructions executable by the processor for causing the transmitter

-   -   in a first mode of operation with a first subcarrier spacing f1:        to transmit a sequence of prefixed OFDM symbols; and    -   in a second mode of operation with a second subcarrier spacing        f2: to transmit a sequence of prefixed OFDM symbols.        The sequence of transmitted OFDM symbols is aligned with a        predefined repeating radio frame, which is common to both the        first and second modes of operation, or with an integer multiple        of the predefined repeating radio frame; and the first and        second subcarrier spacings are related by an integer factor,        f1/f2=p or f1/f2=1/p, with p≠1 integer.

In one embodiment, each predefined repeating radio frame has a length of1 ms and/or is a New Radio (NR) subframe.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of prefixed OFDM symbols transmitted in the secondmode of operation.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of corresponding prefixed OFDM symbols transmittedin the second mode of operation.

In one embodiment, f1/f2=1/p and the integer number is p.

In one embodiment, at least two consecutive symbols in the second modeof operation have prefixes of unequal durations.

In one embodiment, in every 0.5 ms duration in the first or second modeof operation, the first prefixed OFDM symbol has a longer prefix thanany remaining prefixed OFDM symbol(s), and the remaining prefixed OFDMsymbols have prefixes of the same length.

In one embodiment, the duration of a non-prefixed symbol transmitted inthe first mode of operation is constant and the duration of anon-prefixed symbol transmitted in the second mode of operation isconstant.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned, withrespect to the predefined repeating radio frame or a multiple of thepredefined repeating radio frame, with the beginning and end of asequence of an integer number of prefixed OFDM symbols transmitted inthe second mode of operation.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned with thebeginning and end of a sequence of an integer number of prefixed OFDMsymbols transmitted in the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory further stores instructions executable by the processor causingthe transmitter to prefix the OFDM symbols in such manner as to align,with respect to the predefined repeating radio frame, boundaries of atleast some OFDM symbols transmitted in the first mode of operation withboundaries of at least some OFDM symbols transmitted in the second modeof operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory further stores instructions executable by the processor causingthe transmitter to prefix the OFDM symbols in such manner as to alignboundaries of at least some OFDM symbols transmitted in the first modeof operation with boundaries of at least some OFDM symbols transmittedin the second mode of operation.

In one embodiment, alignment of boundaries occurs at least as often asthe predefined repeating radio frame repeats.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory further stores instructions executable by the processor causingthe transmitter to assign prefixes of such lengths as to make the totalduration of a first integer number N₁ of prefixed OFDM symboltransmitted in the first mode of operation equal to a total duration ofa second integer number N₂ of prefixed OFDM symbols transmitted in thesecond mode of operation.

In one embodiment, the first integer number N₁ is 1 and the secondinteger number N₂ is greater than 1.

In one embodiment, with respect to the predefined repeating radio frame,a not-frame-initial boundary of a symbol transmitted in the first modeof operation is aligned with a not-frame-initial boundary of a symboltransmitted in the second mode of operation.

In one embodiment, the first and second subcarrier spacings are relatedby a power of two, f1/f2=2^(q) or f1/f2=2^(−q), with q≠1 integer.

In one embodiment, the first radio node is further operable in a thirdmode of operation with a third subcarrier spacing, wherein the first andthird subcarrier spacings are related by a power of two, f1/f3=2^(r) orf1/f3=2^(−r), with r≠1 integer.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2 is a regular 3GPP LTE subcarrier spacing.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2=15 kHz.

In one embodiment, when the first subcarrier spacing f1=15 kHz, thesecond subcarrier spacing f2<15 kHz, or when the second subcarrierspacing f2=15 kHz, the first subcarrier spacing f1<15 kHz.

In one embodiment, the memory further stores instructions executable bythe processor for causing the transmitter to transmit, in a samepredefined repeating radio frame, at least one prefixed OFDM symbol inthe first mode of operation and at least two OFDM prefixed symbols inthe second mode of operation.

In one embodiment, a ratio of the first and second subcarrier spacingsf1/f2 is equal to an inverse ratio of respective durations t1/t2 ofnon-prefixed OFDM symbols in the first and second modes of operation,f1/f2=t2/t1.

In one embodiment, the first radio node is a wireless device.

In one embodiment, the first radio node is a network node.

According to a second aspect of the present disclosure, there isprovided a method in an orthogonal frequency division multiplexing(OFDM) first radio node. The method comprises: transmitting, in a firstmode of operation with a first subcarrier spacing f1, a sequence ofprefixed OFDM symbols; and transmitting, in a second mode of operationwith a second subcarrier spacing f2, a sequence of prefixed OFDMsymbols. The sequence of transmitted OFDM symbols is aligned with apredefined repeating radio frame, which is common to both the first andsecond modes of operation, or with an integer multiple of the predefinedrepeating radio frame; and the first and second subcarrier spacings arerelated by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer.

In one embodiment, the method further comprises alternating between thefirst and second modes of operation.

In one embodiment, said alternating is performed inside one radio frame.

According to a third aspect of the present disclosure, there is provideda second radio node configured for orthogonal frequency divisionmultiplexing (OFDM). The second radio node comprises a receiver, atransmitter, a processor and a memory storing instructions executable bythe processor for causing the receiver

-   -   in a first mode of operation with a first subcarrier spacing f1:        to receive a sequence of prefixed OFDM symbols from a first        radio node, and in a second mode of operation with a second        subcarrier spacing f2: to receive a sequence of prefixed OFDM        symbols from a first radio node.        The receiver receives the sequence of received OFDM symbols        assuming it to be nominally aligned with a predefined repeating        radio frame, which is common to both the first and second modes        of operation, or with an integer multiple of the predefined        repeating radio frame; and the first and second subcarrier        spacings are related by an integer factor, f1/f2=p or f1/f2=1/p,        with p≠1 integer.

In one embodiment, each predefined repeating radio frame has a length of1 ms and/or is a New Radio, NR, subframe.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of prefixed OFDM symbols transmitted in the secondmode of operation.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of corresponding prefixed OFDM symbols transmittedin the second mode of operation.

In one embodiment, f1/f2=1/p and the integer number is p.

In one embodiment, at least two consecutive symbols in the second modeof operation have prefixes of unequal durations.

In one embodiment, in every 0.5 ms duration in the first or second modeof operation, the first prefixed OFDM symbol has a longer prefix thanany remaining prefixed OFDM symbol(s), and the remaining prefixed OFDMsymbols have prefixes of the same length.

In one embodiment, the duration of a non-prefixed symbol transmitted inthe first second mode of operation is constant and the duration of anon-prefixed symbol transmitted in the second mode of operation isconstant.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned, withrespect to the predefined repeating radio frame or a multiple of thepredefined repeating radio frame, with the beginning and end of asequence of an integer number of prefixed OFDM symbols transmitted inthe second mode of operation.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned with thebeginning and end of a sequence of an integer number of prefixed OFDMsymbols transmitted in the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory further stores instructions executable by the processor to theeffect that the received OFDM symbols have nominally been prefixed insuch manner as to align, with respect to the predefined repeating radioframe, boundaries of at least some OFDM symbols transmitted in the firstmode of operation with boundaries of at least some OFDM symbolstransmitted in the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory further stores instructions executable by the processor to theeffect that the received OFDM symbols have nominally been prefixed insuch manner as to align boundaries of at least some OFDM symbolstransmitted in the first mode of operation with boundaries of at leastsome OFDM symbols transmitted in the second mode of operation.

In one embodiment, alignment of boundaries occurs at least as often asthe predefined repeating radio frame repeats.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory further stores instructions executable by the processor to theeffect that the received OFDM symbols have nominally been assignedprefixes of such lengths as to make the total duration of a firstinteger number N₁ of prefixed OFDM symbol transmitted in the first modeof operation equal to a total duration of a second integer number N₂ ofprefixed OFDM symbols transmitted in the second mode of operation.

In one embodiment, the first integer number N₁ is 1 and the secondinteger number N₂ is greater than 1.

In one embodiment, with respect to the predefined repeating radio frame,a not-frame-initial boundary of a symbol transmitted in the first modeof operation is nominally aligned with a not-frame-initial boundary of asymbol transmitted in the second mode of operation.

In one embodiment, the first and second subcarrier spacings are relatedby a power of two, f1/f2=2^(q) or f1/f2=2^(−q), with q≠1 integer.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2 is a regular 3GPP LTE subcarrier spacing.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2=15 kHz.

In one embodiment, when the first subcarrier spacing f1=15 kHz, thesecond subcarrier spacing f2<15 kHz, or when the second subcarrierspacing f2=15 kHz, the first subcarrier spacing f1<15 kHz.

In one embodiment, the memory further stores instructions executable bythe processor for causing the receiver to receive, in a same radioframe, at least one OFDM symbol in the first mode of operation and atleast two OFDM symbols in the second mode of operation.

In one embodiment, nominally a ratio of the first and second subcarrierspacings f1/f2 is equal to an inverse ratio of respective durationst1/t2 of non-prefixed OFDM symbols in the first and second modes ofoperation, f1/f2=t2/t1.

In one embodiment, the second radio node is a wireless device.

In one embodiment, the second radio node is a network node.

According to a fourth aspect of the present disclosure, there isprovided a method in an orthogonal frequency division multiplexing(OFDM) second radio node. The method comprises: receiving, in a firstmode of operation with a first subcarrier spacing f1, a sequence ofprefixed OFDM symbols from a first radio node; and receiving, in asecond mode of operation with a second subcarrier spacing f2, a sequenceof prefixed OFDM symbols from a first radio node. The received sequenceof OFDM symbols is assumed to be nominally aligned with a predefinedrepeating radio frame, which is common to both the first and secondmodes of operation, or with an integer multiple of the predefinedrepeating radio frame; and the first and second subcarrier spacings arerelated by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer.

In one embodiment, the method further comprises alternating between thefirst and second modes of operation.

In one embodiment, said alternating is performed inside one radio frame.

According to a fifth aspect of the present disclosure, there is provideda computer program comprising computer-readable instructions for causinga programmable processor to perform the method of the second or fourthaspect of the present disclosure.

According to a sixth aspect of the present disclosure, there is provideda computer program product comprising a computer-readable medium storingthe computer program of the fifth aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentdisclosure will become apparent from the following descriptions onembodiments of the present disclosure with reference to the drawings, onwhich:

FIG. 1 shows subframe designs consisting of OFDM symbols for severaldifferent numerologies with subcarrier spacings higher than 15 kHz;

FIGS. 2a, 2b and 2c show subframe designs consisting of OFDM symbols forseveral different numerologies with subcarrier spacings higher and lowerthan 15 kHz according to embodiments of the present disclosure;

FIG. 3 is a schematic block diagram of radio node 300 according to someembodiments of the present disclosure;

FIG. 4 is a flow chart showing a method 400 in a radio node according tosome embodiments of the present disclosure;

FIG. 5 is a schematic block diagram of radio node 500 according to someembodiments of the present disclosure;

FIG. 6 is a flow chart showing a method 600 in a radio node according tosome embodiments of the present disclosure; and

FIG. 7 schematically shows an embodiment of an arrangement 700 which maybe used in radio node 300/500.

In the drawings, similar or same steps and/or elements are designatedwith similar or same referential numbers. It is to be noted that not allthe steps and/or elements shown in the drawings are necessary for someembodiments of the present disclosure. For simplicity and clarity, thoseoptional steps and/or elements are shown in dashed lines.

DETAILED DESCRIPTION

In the discussion that follows, specific details of particularembodiments of the present techniques are set forth for purposes ofexplanation and not limitation. It will be appreciated by those skilledin the art that other embodiments may be employed apart from thesespecific details. Furthermore, in some instances detailed descriptionsof well-known methods, nodes, interfaces, circuits, and devices areomitted so as not obscure the description with unnecessary detail.

Those skilled in the art will appreciate that the functions describedmay be implemented in one or in several nodes. Some or all of thefunctions described may be implemented using hardware circuitry, such asanalog and/or discrete logic gates interconnected to perform aspecialized function, ASICs, PLAs, etc. Likewise, some or all of thefunctions may be implemented using software programs and data inconjunction with one or more digital microprocessors or general purposecomputers. Where nodes that communicate using the air interface aredescribed, it will be appreciated that those nodes also have suitableradio communications circuitry. Moreover, the technology canadditionally be considered to be embodied entirely within any form ofcomputer-readable memory, including non-transitory embodiments such assolid-state memory, magnetic disk, or optical disk containing anappropriate set of computer instructions that would cause a processor tocarry out the techniques described herein.

Hardware implementations of the presently disclosed techniques mayinclude or encompass, without limitation, digital signal processor (DSP)hardware, a reduced instruction set processor, hardware (e.g., digitalor analog) circuitry including but not limited to application specificintegrated circuit(s) (ASIC) and/or field programmable gate array(s)(FPGA(s)), and (where appropriate) state machines capable of performingsuch functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors or one or more controllers, and theterms computer, processor, and controller may be employedinterchangeably. When provided by a computer, processor, or controller,the functions may be provided by a single dedicated computer orprocessor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, theterm “processor” or “controller” also refers to other hardware capableof performing such functions and/or executing software, such as theexample hardware recited above.

Since various wireless systems may benefit from exploiting the ideascovered within this disclosure as will be appreciated by those skilledin the art, terms like “base station”, “user equipment”, “access point”and “core network node” as used herein should be understood in a broadsense. Specifically, the base station should be understood to encompassa legacy base station in a 2nd Generation (2G) network, a NodeB in a 3rdGeneration (3G) network, an evolved NodeB (eNode B) in a 4th Generation(4G) or future evolved network (e.g., LTE network, LTE-A network etc.),and the like. The user equipment should be understood to encompass amobile telephone, a smartphone, a wireless-enabled tablet or personalcomputer, a wireless machine-to-machine unit, and the like. The accesspoint should be understood to encompass a wireless switch, a wirelessrouter, a wireless hub, a wireless bridge, or any device capable ofbeing used in a wireless local area network for accessingfunctionalities, and the like. The core network node should beunderstood to encompass a Mobility Management Entity (MME), a ServingGPRS Support Node (SGSN), and the like.

According to the present disclosure, it is proposed to select the LTEsubcarrier spacing as the base frequency, f0=15 kHz, and use differentscaling strategy when increasing the subcarrier spacing compared to whendecreasing the sub carrier spacing from this value.

When increasing the subcarrier spacing to 30 kHz, 60 kHz, 120 kHz and soon, each OFDM symbol of the lower numerology (i.e., the one with thelower subcarrier spacing) is split into two equal-length symbols in thehigher numerology (i.e., the one with the higher subcarrier spacing).Note that in this case the “longer” cyclic prefix is located at thebeginning of a 0.5 ms period.

For example, as shown in FIG. 2a , each OFDM symbol of the numerologyhaving subcarrier spacing of 15 kHz can be split into two equal-lengthOFDM symbols of the numerology having subcarrier spacing of 30 kHz, orfour equal-length OFDM symbols of the numerology having subcarrierspacing of 60 kHz. This is also shown in rows “30” and “60” in FIG. 2b ,which shows OFDM symbol durations (including CP) in multiples of LTE Tsover 2 ms. FIG. 2c is a magnified view of FIG. 2b shown in two portions,with the first two 0.5 ms periods (0.5 ms (I) and 0.5 ms (II)) shown inthe upper portion (1) and the following two 0.5 ms periods (0.5 ms (III)and 0.5 ms (IV)) shown in the lower portion (2). Alternatively, as shownin rows “30 alt.” and “60 alt.” in FIG. 2b and FIG. 2c , the first OFDMsymbol of the numerology having subcarrier spacing of 15 kHz can besplit into two OFDM symbols of the numerology having subcarrier spacingof 30 kHz, or four OFDM symbols of the numerology having subcarrierspacing of 60 kHz, with only the first OFDM symbol in every 0.5 ms ofthe numerology having subcarrier spacing of 30 kHz or 60 kHz having the“longer” CP and the other OFDM symbols all having the same duration.

When decreasing the subcarrier spacing from 15 kHz to 7.5 kHz, 3.75 kHz,etc., OFDM symbols in the higher numerology are pairwise concatenated tocreate one OFDM symbol in the lower subcarrier spacing numerology. Thisresults in the longer symbol (in the lower numerology) has a durationequal to two symbols with shorter CP or the sum of one symbol withlonger CP and one symbol with shorter CP. Note that in this case the“longer” cyclic prefix is not necessary at the beginning of a set of a0.5 ms period.

For example, as shown in FIG. 2a , FIG. 2b and FIG. 2c , each OFDMsymbol of the numerology having subcarrier spacing of 3.75 kHz can havea duration equal to two corresponding OFDM symbols of the numerologyhaving subcarrier spacing of 7.5 kHz, or four corresponding OFDM symbolsof the numerology having subcarrier spacing of 15 kHz. In this context,one OFDM symbol of a numerology “corresponds” to two or four OFDMsymbols of another numerology when the one OFDM symbol is aligned withthe two or four OFDM symbols in the sense that they begin and endsimultaneously.

FIG. 3 is a schematic block diagram of radio node 300 according to someembodiments of the present disclosure. The radio node 300 can be eithera wireless device or a network node. The radio node 300 can be used as afirst radio node configured for orthogonal frequency divisionmultiplexing (OFDM). The radio node 300 includes a receiver 310, atransmitter 320, a processor 330 and a memory 340.

The memory 340 stores instructions executable by the processor 330 forcausing the transmitter 320

-   -   in a first mode of operation with a first subcarrier spacing f1,        to transmit a sequence of prefixed OFDM symbols, and    -   in a second mode of operation with a second subcarrier spacing        f2, to transmit a sequence of prefixed OFDM symbols.

The sequence of transmitted OFDM symbols is aligned with a predefinedrepeating radio frame, which is common to both the first and secondmodes of operation, or with an integer multiple of the radio frame; andthe first and second subcarrier spacings are related by an integerfactor, f1/f2=p or f1/f2=1/p, with p≠1 integer. For example, as shown inFIG. 2, the f1 can be 15 kHz, and f2 can be 7.5 kHz or 30 kHz.

In one embodiment, each predefined repeating radio frame has a length of1 ms and/or is a New Radio (NR) subframe.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of prefixed OFDM symbols transmitted in the secondmode of operation.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of corresponding prefixed OFDM symbols transmittedin the second mode of operation. In this context, one OFDM symbol of anumerology “corresponds” to a number of OFDM symbols of anothernumerology when the one OFDM symbol is aligned with the number of OFDMsymbols in the sense that they begin and end simultaneously.

In one embodiment, f1/f2=1/p and the integer number is p.

In one embodiment, at least two consecutive symbols in the second modeof operation have prefixes of unequal durations.

In one embodiment, in every 0.5 ms duration in the first or second modeof operation, the first prefixed OFDM symbol has a longer prefix thanany remaining prefixed OFDM symbol(s), and the remaining prefixed OFDMsymbols have prefixes of the same length. Examples for this can be seenin rows “30 alt” and “60 alt” in FIG. 2b and FIG. 2 c.

In one embodiment, the duration of a non-prefixed symbol transmitted inthe first mode of operation is constant and the duration of anon-prefixed symbol transmitted in the second mode of operation isconstant.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned, withrespect to the predefined repeating radio frame or a multiple of thepredefined repeating radio frame, with the beginning and end of asequence of an integer number of prefixed OFDM symbols transmitted inthe second mode of operation.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned with thebeginning and end of a sequence of an integer number of prefixed OFDMsymbols transmitted in the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory 340 further stores instructions executable by the processor 330causing the transmitter 320 to prefix the OFDM symbols in such manner asto align, with respect to the predefined repeating radio frame,boundaries of at least some OFDM symbols transmitted in the first modeof operation with boundaries of at least some OFDM symbols transmittedin the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory 340 further stores instructions executable by the processor 320causing the transmitter 320 to prefix the OFDM symbols in such manner asto align boundaries of at least some OFDM symbols transmitted in thefirst mode of operation with boundaries of at least some OFDM symbolstransmitted in the second mode of operation.

In one embodiment, alignment of boundaries occurs at least as often asthe predefined repeating radio frame repeats.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory 340 further stores instructions executable by the processor 330causing the transmitter 320 to assign prefixes of such lengths as tomake the total duration of a first integer number N₁ of prefixed OFDMsymbol transmitted in the first mode of operation equal to a totalduration of a second integer number N₂ of prefixed OFDM symbolstransmitted in the second mode of operation.

In one embodiment, the first integer number N₁ is 1 and the secondinteger number N₂ is greater than 1.

In one embodiment, with respect to the predefined repeating radio frame,a not-frame-initial boundary of a symbol transmitted in the first modeof operation is aligned with a not-frame-initial boundary of a symboltransmitted in the second mode of operation.

In one embodiment, the first and second subcarrier spacings are relatedby a power of two, f1/f2=2^(q) or f1/f2=2^(−q), with q≠1 integer.

In one embodiment, the first radio node 300 is further operable in athird mode of operation with a third subcarrier spacing, wherein thefirst and third subcarrier spacings are related by a power of two,f1/f3=2^(r) or f1/f3=2^(−r), with r≠1 integer.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2 is a regular 3GPP LTE subcarrier spacing.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2=15 kHz.

In one embodiment, when the first subcarrier spacing f1=15 kHz, thesecond subcarrier spacing f2<15 kHz, or when the second subcarrierspacing f2=15 kHz, the first subcarrier spacing f1<15 kHz.

In one embodiment, the memory 340 further stores instructions executableby the processor 330 for causing the transmitter 320 to transmit, in asame predefined repeating radio frame, at least one prefixed OFDM symbolin the first mode of operation and at least two OFDM prefixed symbols inthe second mode of operation.

In one embodiment, a ratio of the first and second subcarrier spacingsf1/f2 is equal to an inverse ratio of respective durations t1/t2 ofnon-prefixed OFDM symbols in the first and second modes of operation,f1/f2=t2/t1.

FIG. 4 is a flow chart showing a method 400 in a radio node according tosome embodiments of the present disclosure.

The method 400 comprises steps S410 and S420. In step S410, the radionode is in a first mode of operation with a first subcarrier spacing f1,a sequence of prefixed OFDM symbols is transmitted. In step S420, theradio node is in a second mode of operation with a second subcarrierspacing f2, a sequence of prefixed OFDM symbols is transmitted. In themethod 400, the sequence of transmitted OFDM symbols is aligned with apredefined repeating radio frame, which is common to both the first andsecond modes of operation, or with an integer multiple of the predefinedrepeating radio frame; and the first and second subcarrier spacings arerelated by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer.

In one embodiment, the method 400 further includes a step S430 ofalternating between the first and second modes of operation(double-ended arrow in FIG. 4). Furthermore, said alternating isperformed inside one radio frame.

FIG. 5 is a schematic block diagram of radio node 500 according to someembodiments of the present disclosure. The radio node 500 can be eithera wireless device or a network node. The radio node 500 can be used as asecond radio node configured for orthogonal frequency divisionmultiplexing (OFDM). The radio node 500 includes a receiver 510, atransmitter 520, a processor 530 and a memory 540.

The memory 540 stores instructions executable by the processor 530 forcausing the receiver 510

-   -   in a first mode of operation with a first subcarrier spacing f1:        to receive a sequence of prefixed OFDM symbols from a first        radio node, and    -   in a second mode of operation with a second subcarrier spacing        f2: to receive a sequence of prefixed OFDM symbols from a first        radio node.        The receiver 510 receives the sequence of received OFDM symbols        assuming it to be nominally aligned with a predefined repeating        radio frame, which is common to both the first and second modes        of operation, or with an integer multiple of the predefined        repeating radio frame; and the first and second subcarrier        spacings are related by an integer factor, f1/f2=p or f1/f2=1/p,        with p≠1 integer. For example, as shown in FIG. 2, the f1 can be        15 kHz, and f2 can be 7.5 kHz or 30 kHz.

In one embodiment, each predefined repeating radio frame has a length of1 ms and/or is a New Radio, NR, subframe.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of prefixed OFDM symbols transmitted in the secondmode of operation.

In one embodiment, a total duration of one prefixed OFDM symboltransmitted in the first mode of operation is equal to a total durationof an integer number of corresponding prefixed OFDM symbols transmittedin the second mode of operation.

In one embodiment, f1/f2=1/p and the integer number is p.

In one embodiment, at least two consecutive symbols in the second modeof operation have prefixes of unequal durations.

In one embodiment, in every 0.5 ms duration in the first or second modeof operation, the first prefixed OFDM symbol has a longer prefix thanany remaining prefixed OFDM symbol(s), and the remaining prefixed OFDMsymbols have prefixes of the same length. Examples for this can be seenin rows “30 alt.” and “60 alt.” in FIG. 2b and FIG. 2 c.

In one embodiment, the duration of a non-prefixed symbol transmitted inthe first second mode of operation is constant and the duration of anon-prefixed symbol transmitted in the second mode of operation isconstant.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned, withrespect to the predefined repeating radio frame or a multiple of thepredefined repeating radio frame, with the beginning and end of asequence of an integer number of prefixed OFDM symbols transmitted inthe second mode of operation.

In one embodiment, the beginning and end of said one prefixed OFDMsymbol transmitted in the first mode of operation are aligned with thebeginning and end of a sequence of an integer number of prefixed OFDMsymbols transmitted in the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory 540 further stores instructions executable by the processor 530to the effect that the received OFDM symbols have nominally beenprefixed in such manner as to align, with respect to the predefinedrepeating radio frame, boundaries of at least some OFDM symbolstransmitted in the first mode of operation with boundaries of at leastsome OFDM symbols transmitted in the second mode of operation.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory 540 further stores instructions executable by the processor 530to the effect that the received OFDM symbols have nominally beenprefixed in such manner as to align boundaries of at least some OFDMsymbols transmitted in the first mode of operation with boundaries of atleast some OFDM symbols transmitted in the second mode of operation.

In one embodiment, alignment of boundaries occurs at least as often asthe predefined repeating radio frame repeats.

In one embodiment, a total duration t1 of one non-prefixed OFDM symbolin the first mode of operation is an integer multiple of a duration t2of one non-prefixed OFDM symbol in the second mode of operation. Thememory 540 further stores instructions executable by the processor 530to the effect that the received OFDM symbols have nominally beenassigned prefixes of such lengths as to make the total duration of afirst integer number N₁ of prefixed OFDM symbol transmitted in the firstmode of operation equal to a total duration of a second integer numberN₂ of prefixed OFDM symbols transmitted in the second mode of operation.

In one embodiment, the first integer number N₁ is 1 and the secondinteger number N₂ is greater than 1.

In one embodiment, with respect to the predefined repeating radio frame,a not-frame-initial boundary of a symbol transmitted in the first modeof operation is nominally aligned with a not-frame-initial boundary of asymbol transmitted in the second mode of operation.

In one embodiment, the first and second subcarrier spacings are relatedby a power of two, f1/f2=2^(q) or f1/f2=2^(−q), with q≠1 integer.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2 is a regular 3GPP LTE subcarrier spacing.

In one embodiment, the first subcarrier spacing f1 or the secondsubcarrier spacing f2=15 kHz.

In one embodiment, when the first subcarrier spacing f1=15 kHz, thesecond subcarrier spacing f2<15 kHz, or when the second subcarrierspacing f2=15 kHz, the first subcarrier spacing f1<15 kHz.

In one embodiment, the memory 540 further stores instructions executableby the processor 530 for causing the receiver 510 to receive, in a sameradio frame, at least one OFDM symbol in the first mode of operation andat least two OFDM symbols in the second mode of operation.

In one embodiment, nominally a ratio of the first and second subcarrierspacings f1/f2 is equal to an inverse ratio of respective durationst1/t2 of non-prefixed OFDM symbols in the first and second modes ofoperation, f1/f2=t2/t1.

FIG. 6 is a flow chart showing a method 600 in a radio node according tosome embodiments of the present disclosure.

The method 600 comprises steps S610 and S620. In step S610, the radionode is in a first mode of operation with a first subcarrier spacing f1,a sequence of prefixed OFDM symbols is received from a first radio node.In step S620, the radio node is in a second mode of operation with asecond subcarrier spacing f2, a sequence of prefixed OFDM symbols isreceived from a first radio node. In the method 600, the receivedsequence of OFDM symbols is assumed to be nominally aligned with apredefined repeating radio frame, which is common to both the first andsecond modes of operation, or with an integer multiple of the predefinedrepeating radio frame; and the first and second subcarrier spacings arerelated by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer.

In one embodiment, the method 600 further includes a step S630 ofalternating between the first and second modes of operation(double-ended arrow in FIG. 6). Furthermore, said alternating isperformed inside one radio frame.

FIG. 7 schematically shows an embodiment of an arrangement 700 which maybe used in radio node 300/500.

Comprised in the arrangement 700 are here a processing unit 706, e.g.,with a Digital Signal Processor (DSP). The processing unit 706 may be asingle unit or a plurality of units to perform different actions ofprocedures described herein. The arrangement 700 may also comprise aninput unit 702 for receiving signals from other entities, and an outputunit 704 for providing signal(s) to other entities. The input unit andthe output unit may be arranged as an integrated entity or asillustrated in the example of FIG. 7.

Furthermore, the arrangement 700 comprises at least one computer programproduct 708 in the form of a non-volatile or volatile memory, e.g., anElectrically Erasable Programmable Read-Only Memory (EEPROM), a flashmemory and a hard drive. The computer program product 708 comprises acomputer program 710, which comprises code/computer readableinstructions, which when executed by the processing unit 706 in thearrangement 700 causes the arrangement 700 and/or the radio node inwhich it is comprised to perform the actions, e.g., of the proceduredescribed earlier in conjunction with FIG. 4 and/or FIG. 6.

The computer program 710 may be configured as a computer program codestructured in computer program modules 710 a-710 c.

Hence, in exemplifying embodiments corresponding to FIG. 4, the code inthe computer program 710 of the arrangement 700 comprises first modeoperation module 710 a for causing the output unit 704 to transmit, in afirst mode of operation with a first subcarrier spacing f1, a sequenceof prefixed OFDM symbols; and second mode operation module 710 b forcausing the output unit 704 to transmit, in a second mode of operationwith a second subcarrier spacing f2: to transmit a sequence of prefixedOFDM symbols. Alternating module 710 c is optional for causing theoutput unit 704 to alternate between the first and second modes ofoperation.

In exemplifying embodiments corresponding to FIG. 6, the code in thecomputer program 710 of the arrangement 700 comprises first modeoperation module 710 a for causing the input unit 702 to receive, in afirst mode of operation with a first subcarrier spacing f1, a sequenceof prefixed OFDM symbols from a first radio node; and second modeoperation module 710 b for causing the input unit 702 to receive, in asecond mode of operation with a second subcarrier spacing f2, a sequenceof prefixed OFDM symbols from a first radio node. Alternating module 710c is optional for causing the input unit 702 to alternate between thefirst and second modes of operation.

Although the code means in the embodiments disclosed above inconjunction with FIG. 7 are implemented as computer program moduleswhich when executed in the processing unit causes the device to performthe actions described above in conjunction with the figures mentionedabove, at least one of the code means may in alternative embodiments beimplemented at least partly as hardware circuits.

The processor may be a single CPU (Central processing unit), but couldalso comprise two or more processing units. For example, the processormay include general purpose microprocessors; instruction set processorsand/or related chips sets and/or special purpose microprocessors such asApplication Specific Integrated Circuits (ASICs). The processor may alsocomprise board memory for caching purposes. The computer program may becarried by a computer program product connected to the processor. Thecomputer program product may comprise a computer readable medium onwhich the computer program is stored. For example, the computer programproduct may be a flash memory, a Random-access memory (RAM), a Read-OnlyMemory (ROM), or an EEPROM, and the computer program modules describedabove could in alternative embodiments be distributed on differentcomputer program products in the form of memories within the UE.

In an embodiment of the present disclosure, there is provided acomputer-readable storage medium (e.g., computer program product 708)storing instructions that when executed, cause one or more computingdevices to perform the methods according to the present disclosure.

Although the present technology has been described above with referenceto specific embodiments, it is not intended to be limited to thespecific form set forth herein. For example, the embodiments presentedherein are not limited to the existing NR/LTE configuration; rather theyare equally applicable to new NR/LTE configurations defined in future.The technology is limited only by the accompanying claims and otherembodiments than the specific above are equally possible within thescope of the appended claims. As used herein, the terms“comprise/comprises” or “include/includes” do not exclude the presenceof other elements or steps. Furthermore, although individual featuresmay be included in different claims, these may possibly advantageouslybe combined, and the inclusion of different claims does not imply that acombination of features is not feasible and/or advantageous. Inaddition, singular references do not exclude a plurality. Finally,reference signs in the claims are provided merely as a clarifyingexample and should not be construed as limiting the scope of the claimsin any way.

Note on NR terminology

The 3GPP has issued agreements concerning NR terminology in the periodbetween the earliest priority date and the filing date of the presentdisclosure. NR terminology and LTE terminology coincide to aconsiderable extent; for instance, a resource element (RE) remains 1subcarrier×1 OFDM symbol. Yet some terms known in LTE have been given anew meaning in NR. This disclosure, including the claims, appliesprefixes “LTE” and “NR” when indefiniteness could otherwise arise.Examples: An LTE subframe lasting 1 ms contains 14 OFDM symbols fornormal CP. An NR subframe has a fixed duration of 1 ms and may thereforecontain a different number of OFDM symbols for different subcarrierspacings. An LTE slot corresponds to 7 OFDM symbols for normal CP. An NRslot corresponds to 7 or 14 OFDM symbols; at 15 kHz subcarrier spacing,a slot with 7 OFDM symbols occupies 0.5 ms. Concerning NR terminology,reference is made to 3GPP TR 38.802 v14.0.0 and later versions.

A non-prefixed term in this disclosure is to be understood in the LTEsense unless otherwise stated. However, any term designating an objector operation known from LTE is expected to be reinterpreted functionallyin view of NR specifications. Examples: An LTE radio frame may befunctionally equivalent to an NR frame, considering that both have aduration of 10 ms. An LTE eNB may be functionally equivalent to an NRgNB, since their functionalities as downlink transmitter are at leastpartially overlapping. The least schedulable resource unit in LTE may bereinterpreted as the least schedulable resource unit in NR. The shortestdata set for which LTE acknowledgement feedback is possible may bereinterpreted as the shortest data set for which NR acknowledgementfeedback is possible.

Therefore, even though some embodiments of this disclosure have beendescribed using LTE-originated terminology, they remain fully applicableto NR technology.

What is claimed is:
 1. A first radio node configured for orthogonalfrequency division multiplexing, OFDM, comprising: a receiver; atransmitter; a processing circuitry operatively connected to thetransmitter and receiver, the processing circuitry being configured to:transmit a sequence of prefixed OFDM symbols in a first mode ofoperation with a first subcarrier spacing f1 or in a second mode ofoperation with a second subcarrier spacing f2; wherein the first andsecond subcarrier spacings are related by a non-unit integer factor,f1/f2=p or f1/f2=1/p, with p≠1 integer; wherein the sequence of prefixedOFDM symbols is aligned with a predefined repeating radio frame, whichis common to both the first and second modes of operation, or with aninteger multiple of the predefined repeating radio frame; wherein, in arepeating interval in the first and second mode of operation, an initialprefixed OFDM symbol has a longer prefix than any remaining prefixedOFDM symbol(s) in the repeating interval, and the remaining prefixedOFDM symbols in the repeating interval have prefixes of the same length;and wherein boundaries of one prefixed OFDM symbol according to thefirst mode of operation are aligned with boundaries of two or more ofthe prefixed OFDM symbols according to the second mode of operation. 2.The first radio node of claim 1, wherein a total duration of oneprefixed OFDM symbol transmitted in the first mode of operation is equalto a total duration of an integer number of prefixed OFDM symbolstransmitted in the second mode of operation.
 3. The first radio node ofclaim 1, wherein the repeating interval is 0.5 ms.
 4. The first radionode of claim 1, wherein the beginnings and ends of the prefixed OFDMsymbols transmitted in the first mode of operation are aligned, withrespect to the predefined repeating radio frame or a multiple of thepredefined repeating radio frame, with the beginning and end of asequence of an integer number of prefixed OFDM symbols transmitted inthe second mode of operation.
 5. The first radio node of claim 1,wherein the beginnings and ends of the prefixed OFDM symbols transmittedin the first mode of operation are aligned with the beginning and end ofa sequence of an integer number of prefixed OFDM symbols transmitted inthe second mode of operation.
 6. The first radio node of claim 1,wherein alignment of boundaries occurs at least as often as thepredefined repeating radio frame repeats.
 7. The first radio node ofclaim 1, wherein the processing circuitry is further configured toassign prefixes of such lengths as to make a total duration of a firstinteger number N₁ of prefixed OFDM symbol transmitted in the first modeof operation equal to a total duration of a second integer number N₂ ofprefixed OFDM symbols transmitted in the second mode of operation. 8.The first radio node of claim 1, wherein, with respect to the predefinedrepeating radio frame, a not-frame-initial boundary of a symboltransmitted in the first mode of operation is aligned with anot-frame-initial boundary of a symbol transmitted in the second mode ofoperation.
 9. The first radio node of claim 1, wherein the first andsecond subcarrier spacings are related by a power of two, f1/f2=2^(q) orf1/f2=2^(−q), with q≥1 integer.
 10. The first radio node of claim 1,wherein, in a repeating interval in both the first mode of operation andthe second mode of operation, an initial prefixed OFDM symbol in thesequence of prefixed OFDM symbols has a longer prefix than any remainingprefixed OFDM symbol(s) in the repeating interval, and the remainingprefixed OFDM symbols have prefixes of the same length.
 11. A method inan orthogonal frequency division multiplexing (OFDM) first radio node,the method comprising: transmitting, in a first mode of operation with afirst subcarrier spacing f1 or in a second mode of operation with asecond subcarrier spacing f2, a sequence of prefixed OFDM symbols;wherein the sequence of prefixed OFDM symbols is aligned with apredefined repeating radio frame, which is common to both the first andsecond modes of operation, or with an integer multiple of the predefinedrepeating radio frame; wherein the first and second subcarrier spacingsare related by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1integer; wherein in a repeating interval in the first and second mode ofoperation, an initial prefixed OFDM symbol has a longer prefix than anyremaining prefixed OFDM symbol(s) in the repeating interval, and theremaining prefixed OFDM symbols in the repeating interval have prefixesof the same length; and wherein boundaries of one prefixed OFDM symbolaccording to the first mode of operation are aligned with boundaries oftwo or more of the prefixed OFDM symbols according to the second mode ofoperation.
 12. A second radio node configured for orthogonal frequencydivision multiplexing, OFDM, comprising: a receiver; a transmitter; anda processing circuitry operatively connected to the transmitter andreceiver, the processing circuitry being configured to: receive, in afirst mode of operation with a first subcarrier spacing f1 or in asecond mode of operation with a second subcarrier spacing f2, a sequenceof prefixed OFDM symbols from a first radio node; wherein transmissionof the received sequence of prefixed OFDM symbols is assumed to havebeen aligned with a predefined repeating radio frame, which is common toboth the first and second modes of operation, or with an integermultiple of the predefined repeating radio frame; wherein the first andsecond subcarrier spacings are related by an integer factor, f1/f2=p orf1/f2=1/p, with p≠1 integer; wherein in a repeating interval in thefirst and second mode of operation, an initial prefixed OFDM symbol hasa longer prefix than any remaining prefixed OFDM symbol(s) in therepeating interval, and the remaining prefixed OFDM symbols in therepeating interval have prefixes of the same length; and whereinboundaries of one prefixed OFDM symbol according to the first mode ofoperation are aligned with boundaries of two or more of the prefixedOFDM symbols according to the second mode of operation.
 13. A method inan orthogonal frequency division multiplexing, OFDM, second radio node,the method comprising: receiving, in a first mode of operation with afirst subcarrier spacing f1 or in a second mode of operation with asecond subcarrier spacing f2, a sequence of prefixed OFDM symbols from afirst radio node; wherein transmission of the received sequence ofprefixed OFDM symbols is assumed to have been aligned with a predefinedrepeating radio frame, which is common to both the first and secondmodes of operation, or with an integer multiple of the predefinedrepeating radio frame; wherein the first and second subcarrier spacingsare related by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1integer; wherein in a repeating interval in the first and second mode ofoperation, an initial prefixed OFDM symbol has a longer prefix than anyremaining prefixed OFDM symbol(s) in the repeating interval, and theremaining prefixed OFDM symbols in the repeating interval have prefixesof the same length; and wherein boundaries of one prefixed OFDM symbolaccording to the first mode of operation are aligned with boundaries oftwo or more of the prefixed OFDM symbols according to the second mode ofoperation.